The present invention relates to improved catalysts for use in the hydroxylation of benzene or derivatives thereof to form phenol or related compounds.
Phenol or a derivative thereof can be produced by a single-step oxidative hydroxylation of benzene or a derivative thereof, using nitrous oxide over a zeolite catalyst. For example, PCT publication WO 95/27560 describes such a process that employs a zeolite catalyst whose performance is enhanced by hydrothermal treatment. The zeolite catalyst is treated with a water vapor-containing gas phase at a temperature in the range of 350 to 950.degree. C.
A need exists for catalysts having improved performance, so that the conversion of an aromatic hydrocarbon such as benzene to phenol or another desired product can be made more economical. One potential way of improving catalyst performance is by selective introduction of sites for hydroxylation, for example by introducing iron into the catalyst. Introduction of iron into zeolites can be done either during the crystallization (synthesis) of the zeolite or by some post-synthesis technique. Introduction of active iron via synthesis can present complications due to longer crystallization times and introduction of iron into sites which are not responsible for productive pathways. Therefore, post-synthesis introduction of iron is potentially attractive because it avoids the need to develop new crystallization techniques. However, post-synthesis methods have not been entirely satisfactory so far, in part because not all post-synthesis methods permit selective introduction of iron.